Activate Urza by paying {4}, creating a token copy of Training Grounds that is a 1/1 Soldier in addition to its other types.
 Activate Urza by paying {2}, creating a token copy of Training Grounds that is a 1/1 Soldier in addition to its other types.
Activate Urza by paying {1}, creating a token copy of Crumbling Vestige that is a 1/1 Soldier in addition to its other types.
When the Crumbling Vestige token enters the battlefield, it triggers, adding {1}.
Repeat from step 3.

Infinite ETB

Infinite landfall triggers

Infinite tapped creature tokens

Urza, Prince of Kroog

Mycosynth Lattice

Training Grounds

Crumbling Vestige

Activate Urza by paying {4}, creating a token copy of Biomancer's Familiar that is a 1/1 Soldier in addition to its other types.
 Activate Urza by paying {2}, creating a token copy of Biomancer's Familiar that is a 1/1 Soldier in addition to its other types.
Activate Urza by paying {1}, creating a token copy of Crumbling Vestige that is a 1/1 Soldier in addition to its other types.
When the Crumbling Vestige token enters the battlefield, it triggers, adding {1}.
Repeat from step 3.

Combos with "Crumbling Vestige"